This invention relates to high solids thermosetting protective coatings and particularly to polyester or acrylic copolymer high solids coatings containing an adhesion promoter based on an isocyanate modified polyester polymer. High solids coatings are non-aqueous coatings containing minor amounts of organic solvents and are particularly useful as coatings on appliances, aluminum extrusions, general metal surfaces, plastic and wood substrates.
Acrylic polymers are known to generally provide useful coatings exhibiting good film properties. These polymers can contain reactive functional groups which are coreactive with other polymers or resins to provide thermosetting binder systems. Such acrylic binders can be produced by solution or bulk polymerization of ethylenically unsaturated monomers including acrylic monomers. Solvent can be added in minor amounts to render the acrylic polymer fluent. Various acrylic polymers have been suggested to provide high solids polymeric compositions such as disclosed in U.S. Pat. No. 4,374,164, or combined other polymers such as suggested in U.S. Pat. Nos. 4,397,989 or 4,369,283. Copending and commonly assigned U.S. Ser. No. 836,744 filed Mar. 6, 1986 discloses low molecular weight acrylic copolymers combined with low molecular weight polyester polymer to provide high solids coatings whereas U.S. Pat. No. 4,397,989 discloses a high molecular weight acrylic copolymer in conjunction with a polyester polymer to provide acrylic high solids coatings.
It now has been found that acrylic copolymer high solids coatings can be formulated to provide excellent adhesion to plastic substrates by including an isocyanate modified polyester polymer in the coatings. The adhesion promoter comprises a polyester-urethane polymer of moderately high molecular weight and low hydroxyl functionality and provides substantially improved adhesion to plastic substrates such as polyvinyl chloride, polycarbonate, ABS, Noryl, polystyrene and various polymer blends and alloys. These and other advantages of this invention will become more apparent by referring to the detailed description of the invention along with the illustrative examples.